Myenteric plexus

Hirschsprung s disease have ETB receptor mutations). The lack of ET-3/ETB receptor results in the absence of parasympathic ganglionic neurons in the myenteric plexus (Auerbach). Mice with an ET-3/ETB receptor disruption die within 2 weeks after birth. In transgenic mice, in which the expression of the ETB receptor is driven by the dopamine (3-hydroxylase promoter, normal myenteric plexus are present and no enteric disorder develops. These mice, however, show a salt-sensitive hypertension, which can be efficiently treated with amiloride, indicating that ETB receptors are involved in the regulation of natriuresis via the amilorid-sensitive sodium channel ENaC. 

Peripheral Cholinergic heteroreceptor -myenteric plexus Peripheral Vascular smooth muscle, autonomic terminals Peripheral autonomic and trigeminal nerve terminals Peripheral None identified ... 

Peripheral Gl, vascular and bronchial smooth muscle, vascular endothelium, platelets Peripheral Smooth muscle of ileum, stomach fundus (rat), uterus, vasculature, endothelium Peripheral None identified Peripheral Post-ganglionic sympathetic neurons, sensory neurons Peripheral Cardiac muscle, post-ganglionic parasympathetic neurons (myenteric plexus), esophageal and vascular smooth muscle... 

Enteric nerves control intestinal smooth muscle action and are connected to the brain by the autonomic nervous system. IBS is thought to result from dysregulation of this brain-gut axis. The enteric nervous system is composed of two gan-glionated plexuses that control gut innervation the submucous plexus (Meissner s plexus) and the myenteric plexus (Auerbach s plexus). The enteric nervous system and the central nervous system (CNS) are interconnected and interdependent. A number of neurochemicals mediate their function, including serotonin (5-hydroxytryptamine or 5-HT), acetylcholine, substance P, and nitric oxide, among others. 

Pertwee RGS, L. A. Elrick DB, Mechoulam R, Corbett AD. Inhibitory effects of certain enantiomeric cannabinoids in the mouse vas deferens and the myenteric plexus preparation of guinea-pig small intestine. Br J Pharmacol 1992 105 980-984. 

Sonsino E, Mouy R, Foucaud P, Cezard JP, Aigrain Y, Bocquet L, et al Intestinal pseudoobstruction related to cytomegalovirus infection of myenteric plexus. N Engl J Med 1984 311 196-197. 

Schobinger-Clement S, Gerber HA, Stall-mach T Autoaggressive inflammation of the myenteric plexus resulting in intestinal pseudoobstruction. Am J Suig Pathol 1999 23 602-606. 

In the periphery, 5-HT4 receptor mRNA is found in vascular smooth muscle. Newly developed drugs that activate 5-HT4 receptors are of interest for their potential in treating cardiac arrhythmia. The 5-HT4 receptor is also located on neurons of the alimentary tract, for example the myenteric plexus of the ileum, and on smooth muscle cells and secretory cells of the gastrointestinal tract, where they evoke secretions and the peristaltic reflex. 5-HT4 receptor agonists (e.g. cisapride, prucalopride, tegaserod) are used therapeutically in the treatment of constipation-predominant irritable bowel syndrome and in functional motility disorders of the upper gastrointestinal tract. 

Electrically stimulated longitudinal muscle/myenteric plexus preparations from guinea-pig ileum (LMMP-GPI)... 

Serotonin 5-HT1A Human cDNA Alzheimer s disease, anxiety, depression, schizophrenia, hypertension, inflammation, pain, migraine, spasticity ulcers, obesity glaucoma Somatodendritic autoreceptor in hippocampus and raphe nuclei, circadian rhythm, somatodendritic heteroreceptor at cholinergic terminals of myenteric plexus... 

Figure 7.1. The effect of ondansetron on contractile responses to 2-methyl-5-HT in the guinea-pig isolated longitudinal muscle myenteric plexus preparation. Symbols indicate control responses (9) or in the presence of ondansetron at 1 x 10- M (O) or 1 x 10 M ( ). Results + S.E.M. of at least four separate observations. Experiments were performed as described by Butler...

NO is also a likely candidate for the NANC messenger of the myenteric plexus of neurons in the gastrointestinal tract, which mediate peristaltic movements. These neurons are rich in NO synthase and inhibitors of this enzyme prevent the nerve-evoked relaxation of the gut [12]. Nitric oxide released from nitroprusside also stimulates ADP ribosylation of glyceradehyde 3-phosphate dehydrogenase [56]. Consequently, there may be a number of enzymes, which are probably Fe-centered, that may be activated by NO. 

It is an anthraquinone laxative. It is not active as such but after oral intake when it reaches colon the bacteria liberate anthrones, which is the active form. Active form acts on myenteric plexus to increase peristalsis. It also inhibits salt and water absorption in colon. 

It is a selective 5-HT agonist. It restores and increases motility throughout gastrointestinal tract. It appears to increase the release of acetylcholine from myenteric plexus of the gut. 

A highly simplified diagram of the intestinal wall and some of the circuitry of the enteric nervous system (ENS). The ENS receives input from both the sympathetic and the parasympathetic systems and sends afferent impulses to sympathetic ganglia and to the central nervous system. Many transmitter or neuromodulator substances have been identified in the ENS see Table 6-1. ACh, acetylcholine AC, absorptive cell CM, circular muscle layer EC, enterochromaffin cell EN, excitatory neuron EPAN, extrinsic primary afferent neuron 5HT, serotonin IN, inhibitory neuron IPAN, intrinsic primary afferent neuron LM, longitudinal muscle layer MP, myenteric plexus NE, norepinephrine NP, neuropeptides SC, secretory cell SMP, submucosal plexus. 

H3 Presynaptic brain, myenteric plexus, other neurons Gi 4- cAMP R-K-Methylhistamine, imetit, immepip Thioperamide, iodophenpropit, clobenpropit,1 tiprolisant1... 

As previously noted, opioids have significant constipating effects (see Chapter 31). They increase colonic phasic segmenting activity through inhibition of presynaptic cholinergic nerves in the submucosal and myenteric plexuses and lead to increased colonic transit time and fecal water absorption. They also decrease mass colonic movements and the gastrocolic reflex. Although all opioids have antidiarrheal effects, central nervous system effects and potential for addiction limit the usefulness of most. 

Stimulant laxatives Bisacodyl, 5-15 mg daily. Senna, dosage varies, consult product labeling Correctol, Dulcolax, Ex-Lax, Senokot, various generic Stimulant laxative actions include direct irritation of intestinal mucosa or stimulation of the myenteric plexus, resulting in peristalsis. These agents may also cause alteration of fluid and electrolyte absorption, resulting in luminal fluid accumulation and bowel evacuation. 

Garaulet, J.V., Laorden, M.L., Milanes, M.V. Effect of chronic administration of dihydropyridine Ca2+ channel ligands on sufentanil-induced tolerance to p- and K-opioid agonists in the guinea pig ileum myenteric plexus, Regulatory Peptides 1996, 63, 1-8. 

Poli, E., Coruzzi, G., Bertaccini, G., 1991. Histamine H3 receptors regulate acetylcholine release from the guinea pig ileum myenteric plexus. Life Sci. 48, PL63-PL68. 

Yau, W.M., Youther, M L., 1993. Selective inhibition of acetylcholine release from myenteric plexus by histamine3 receptor activation. Gastroenterology 104 (Suppl), A605. 

The appearance of mass movements after meals is caused at least partially by gastrocolic and duodenocolic reflexes. These reflexes result from distension of the stomach and duodenum. They can take place, although with decreased intensity, when the autonomic nerves are removed therefore, it is probable that the reflexes are basically transmitted through the myenteric plexus, although reflexes conducted through the autonomic nervous system probably reinforce this direct route of transmission. 

Ordinarily, defecation results from the defecation reflexes, which can be described as follows. When the feces enter the rectum, distension of the rectal wall initiates afferent signals that spread through the myenteric plexus to initiate peristaltic waves in the descending colon, sigmoid, and rectum, forcing feces toward the anus. As the peristaltic wave approaches the anus, the internal anal sphincter is inhibited by the usual phenomenon of receptive relaxation, and if the external anal sphincter is relaxed, defecation will occur. This overall effect is the intrinsic defecation reflex of the colon itself. 

The enteric nervous system (see Chapter 6 Introduction to Autonomic Pharmacology) is composed of interconnected networks of ganglion cells and nerve fibers mainly located in the submucosa (submucosal plexus) and between the circular and longitudinal muscle layers (myenteric plexus). These networks give rise to nerve fibers that connect with the mucosa and deep muscle. Although extrinsic sympathetic and parasympathetic nerves project onto the submucosal and myenteric plexuses, the enteric nervous system can independently regulate gastrointestinal motility and secretion. Afferent fibers present in the mucosa and muscularis connect to cell bodies in the plexuses that mediate local reflexes. 

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